1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method utilized for manufacturing process of semiconductor devices and so forth.
2. Description of the Related Art
In an exposure apparatus and an exposure method utilized for manufacturing process of semiconductor devices, as the semiconductor devices have become finer, pattern defects caused by minute abnormal focus during exposure, ununiformity application of photoresist and the like have been occurred. Such pattern defects result in performance degradation and decreasing in yield, thereby it is necessary to restrain the occurrence.
As a method for restraining the occurrence of the pattern defects, it is conventionally proposed that measurement of a focus value in a plurality of positions within an exposure area of an exposure apparatus is performed, and, based on the focus value, local defocusing caused by foreign material on a rear surface is detected (for example, see Japanese Laid-Open Patent Publication No. 2003-257847). It is further proposed that a tilting value of a wafer stage in the exposure apparatus is measured every time exposure is performed, and defocusing is highly precisely detected based on the tilting value (for example, see Japanese Laid-Open Patent Publication No. 2006-93316).
An example of a conventional exposure apparatus and exposure method is described hereinafter referring to the drawings. FIG. 9 is a schematic structural view showing a principal part of the conventional exposure apparatus. In FIG. 9, exposure light 87 passed through a reduction projection lens 81 forms an image on a wafer 86. A wafer stage 85, on which the wafer 86 is mounted, is comprised to be drivable to Z direction (an optical-axis direction). While, the wafer stage 85 is provided on a wafer stage 84 which is comprised to be movable to X direction and Y direction (horizontal directions). A controller 89 controls driving of the wafer stages 84 and 85.
In a light receiving unit 82, light irradiated from a light emission unit 83 and reflected on the wafer 86 is incoming, thereby a signal according to incident light is generated. Using the signal generated in the light receiving unit 82, a focus detecting module 88 measures distance between an optical image plane of the reduction projection lens 81 and the surface of the wafer 86. A data storage unit 90 stores every kind of data obtained at every exposure shot, and based on the stored data determines existence/nonexistence of defocusing. A recording unit 91 records information of abnormality occurred on the wafer.
FIG. 10 is a flow chart showing a foreign material detecting algorithm performed in the above described exposure apparatus. First, as shown in FIG. 10, the wafer 86 which is an object to be exposed is carried onto the wafer stage 85 (Step 801). Next, the wafer 86 moved onto the wafer stage 85 and a reticle are globally aligned (Step 802). When the alignment is completed, a first exposure shot on the wafer 86 is moved to a projection position of the reduction projection lens 81 (Step 803). At this time, the focus detecting module 88 performs focus measurement for the exposure shot on the wafer 86 (Step 804). A controller 89 drives the wafer stage 85, based on the focus value obtained by the focus measurement, to a state that the surface of the wafer 86 is coincided with the optical image plane of the reduction projection lens 81. Then, a driving volume focus (Z position) and the tilting value for the wafer stage 85 are stored in the data storage unit 90 (Step 805). After that, the exposure to the shot is conducted (Step 806 and Step 807). Until the exposure to all exposure shots (from a first shot to n shot) on the wafer 86 is completed, Step 803 to Step 807 are repeatedly operated (Step 808 Yes). The wafer 86, on which the exposure is completed, is carried out from the exposure apparatus (Step 808 No, Step 809 and Step 811).
When the exposure operation is completed on the wafer 86, the Z position and the tilting value from the first shot to n shot stored on the data storage unit 90 are compared with the predetermined threshold value (Step 810). When the tilting value is higher than the specific threshold value, it is determined that foreign material exists between the rear surface of the wafer and the wafer stage.
The foreign material attached to the rear surface can be detected by performing the above-described process to every wafer which is an object to be exposed.